The present invention relates generally to automotive chain drive systems and, more particularly, to a mechanical blade-type chain tensioner apparatus useful in confined spaces for applying a tensioning force to a chain traveling there past. Prior art blade-type chain tensioning devices include a chain engaging blade or shoe member, typically molded from a resinous plastic material, having a metal spring installed therein to provide the shoe sub-assembly with the necessary rigidity and damping characteristics while taking advantage of the flexibility, low friction, and good wear properties of the plastic shoe.
FIG. 1 shows an exemplary known tensioner apparatus T′ comprising a bracket K typically defined from a metal stamping and a tensioner blade assembly BAS′ operably connected to the bracket. The bracket K is fixedly secured to an associated engine block EB (FIG. 2) as part of a chain drive system that is provided to phase or “time” the rotational position of one or more camshaft sprockets CMS with respect to the rotational position of the crankshaft sprocket CKS. A chain 15 such as a roller/bush chain or inverted tooth chain is engaged with the crankshaft sprocket CKS and the camshaft sprocket(s) CMS and phases/times the camshaft sprocket(s) to the crankshaft sprocket. The crankshaft sprocket CKS rotates in a direction DIR, and the chain 15 includes a taut strand portion 16 and a slack strand portion 17.
In the illustrated embodiment, the known tensioner T′ comprises an optional fixed chain guide portion FG including a fixed guide flange XF that projects transversely from the main wall MW of the bracket K and that is engaged with and supports a fixed chain guide G defined from a polymeric (plastic) material. The fixed chain guide G includes a guide face GF that slidably engages and supports the taut strand 16 of the chain as shown in FIG. 2.
The tensioner T′ further comprises a tensioner portion TP′ for tensioning the slack strand 17. As part of the tensioner portion TP′, the bracket K comprises a pin P that is welded or otherwise securely affixed to the main wall MW and that projects perpendicularly outward therefrom. The bracket K further comprises a support flange TF that projects outwardly from the main wall MW. An end of the support flange TF forms or defines a ramp R, and an outer wall OW extends transversely from an outer end of the ramp R and extends parallel to the main wall MW such that a channel CH is defined between the main wall MW, the outer wall OW, and the ramp R.
The tensioner portion TP′ includes the known tensioner blade assembly BAS′ comprising a one-piece polymeric or “plastic” blade or shoe B′ and a metal spring S releasably connected to the shoe B′. The spring S is typically formed as a leaf spring from a generally rectangular one-piece strip of spring steel that is formed to have an arched shape. A first or pivot end B1′ of the shoe includes a boss or barrel BL′ that includes pivot bore PB′ that is slidably received onto the pivot pin P. The pivot pin P can be replaced by a shoulder bolt or any other suitable fastener that allows rotation of the pivot end B1′ of the shoe B′ relative to the bracket K. An opposite second or free end B2′ of the shoe includes an enlarged foot BF′ that is located in the channel CH and supported on the ramp R. The bracket K thus maintains the blade assembly BAS′ in its proper position with respect to the plane of the chain path while permitting sliding reciprocal translational motion of the second, free end B2′ on the ramp R as indicated by the arrow “TRANS” along with the related rotational movement of the blade assembly BAS′ at the pivot end B1′ as indicated by the arrow labeled “ROTATE” in response to changes in the tension and position of the slack strand 17 of the chain 15 and corresponding oscillatory movement of the slack strand 17 as indicated by the arrow “AMPL.” FIG. 2A is a partial view of the tensioner T′ that shows this operative movement of the blade assembly BAS′ using solid lines for a first position of the blade assembly BAS′ and phantom lines for a second position of the blade assembly BAS′.
FIG. 3 is a front (outside) view of the known tensioner blade assembly BAS′ and FIG. 4 is a rear (inside) view of the blade assembly BAS'. FIGS. 3A and 3B are section views taken at lines 3A-3A and 3B-3B of FIG. 3, respectively. The first and second ends B1′,B2′ of the shoe define respective first and second spring-receiving slots L1′,L2′ for respectively receiving and retaining first and second opposite ends S1,S2 of the spring S. The shoe B′ also includes a central portion B3′ that extends between and interconnects the pivot and free ends B1′,B2′. An upper or outer surface OS′ of the central portion B3′ provides a chain contact surface adapted for being slidably engaged by an associated chain being tensioned, and the chain moves on the outer surface OS′ in a chain travel direction from the pivot end B1′ toward the free end B2′. The central portion B3′ includes a lower or inner surface IS′ that is defined by the underside of the central portion B3′ that is opposite the outer surface OS′. The inner surface IS′ is contacted by an arched central portion S3 of the spring S.
As such, the first and second spring-receiving slots L1′,L2′ and the inner surface IS′ of the shoe central portion B3′ define a spring-receiving slot or region that opens through a front face FF′ of the shoe B′ and that also opens through a rear face RF′ of the shoe. Each slot L1′,L2′ includes an open mouth M′ (FIG. 4) oriented toward the mouth M′ of the other slot L1′,L2′ through which the spring S extends toward the other slot L1′,L2′, i.e., the mouth M′ of the first slot L1′ opens toward the second slot L2′ and the mouth of the second slot L2′ opens toward the first slot L1′.
With particular reference to FIG. 3A, the first end S1 of the spring S is retained in the slot L1′ between a first side wall W1′ and a first installation tab T1′. The first side wall W1′ is located adjacent the shoe front face FF′ and abuts or lies closely adjacent an outer spring edge SE1. The first installation tab T1′ is located adjacent the shoe rear face RF′ and abuts or lies closely adjacent an inner spring edge SE2. The first spring end S1 is captured in the first spring-receiving slot L1′ between the first side wall W1′ and the first installation tab T1′, with minimal clearance between the first spring end S1 and the first side wall W1′ and the first installation tab T1′ to minimize lateral movement of the first spring end S1 between the first side wall W1′ and the first installation tab T1′. An outermost or distal tip of the first end S1 of the spring contacts a first lower wall LW1′ of the slot L1′ that is spaced from and faces the inner surface IS of the shoe central portion B3. Both the first side wall W1′ and the first installation tab T1′ are connected to and project outwardly from the lower wall LW1′ of the slot L1′ and both extend only partially or part-way toward the shoe central portion B3′ such that space or gap is defined between the shoe central portion B3′ and the outermost surface of both the first side wall W1′ and the first installation tab T1′. In the exemplary embodiment, the lower wall LW1′ is provided by an outer surface of the boss or barrel BL′ in which the pivot bore PB′ is defined.
Similarly, as shown in FIG. 3B, the second end S2 of the spring S is retained in the slot L2′ between a second side wall W2′ and a second installation tab T2′. The second side wall W2′ is located adjacent the shoe front face FF′ and abuts or lies closely adjacent the outer spring edge SE1. The second installation tab T2′ is located adjacent the shoe rear face RF′ and abuts or lies closely adjacent the inner spring edge SE2. The second end S2 of the spring S is captured in the slot L2′ between the second side wall W2′ and the second installation tab T2′, with minimal clearance between the second spring end S2 and the second side wall W2′ and the second installation tab T2′ to prevent or at least minimize lateral movement of the second spring end S2 between the second side wall W2′ and the second installation tab T2′. The second end S2 of the spring contacts a second lower wall LW2′ of the slot L2′ that is spaced from and faces the inner surface IS′ of the shoe central portion B3′. Both the second side wall W2′ and the second installation tab T2′ are connected to a project outwardly or upwardly from the lower wall LW2′, and each extends only partially or part-way toward the shoe central portion B3′ such that space is defined between the shoe central portion B3′ and both the second side wall W1′ and the second installation tab T1′.
With continuing reference to FIGS. 3A and 3B, it can be seen that the first and second installation tabs T1′,T2′ each comprise an upper or outer face OF′ that is generally oriented toward and spaced from the inner surface IS′ of the shoe central portion B3′. Each outer face OF′ is dimensioned and conformed to facilitate sliding insertion of the spring S there over between itself and the shoe inner surface IS′ during sliding movement of the spring S into the slots L1′,L2′. In the illustrated example, the respective outer faces OF′ each comprise an inclined face IF′ that begins adjacent the rear face RF′ of the shoe B′ and that extends closer to the inner surface IS′ as it extends inwardly away from the rear face RF′ toward the front face FF′ of the shoe B′. The respective outer faces OF′ each further comprise a flat face FT′ that connects the inclined faces IF to respective lock faces LF′ that lie transverse to the flat face FT′. The transverse lock faces LF′ connect the innermost end of the flat faces FT′ to the respective lower walls LW1′,LW2′. The lock faces LF′ are respectively oriented toward the first and second side walls W1′,W2′ located on the opposite sides of the slots L1′,L2′, such that the installed spring end S1 is captured between the first side wall W1′ and the lock face LF′ of the first locking tab T1′, and the spring end S2 is captured between the second side wall W2′ and the lock face LF′ of the second locking tab T2′.
Between the first and second slots L1′,L2′, the shoe B′ is completely open through both the front face FF′ and rear face RF′ of the shoe B′. It has been deemed beneficial to eliminate all spring-retaining walls or tabs that extend from the inner surface IS′ of the shoe central portion B3′, as these walls/tabs can create stress risers due to the flexing of the shoe central portion during engine operation. As such, the spring S must be contained in the slots L1′,L2′ by only the installation tabs T1′,T2′ and walls W1′,W2′.
To assemble the blade assembly BAS′, the shoe B is resiliently deformed to decrease the radius of the outer surface OS′ by decreasing the distance between the first and second shoe ends B1′,B2′, which causes the spring-receiving region to temporarily assume a shape that approximates the free (undeflected) shape of the spring S. The first and second spring ends S1,S2 are then inserted simultaneously into the first and second spring-receiving slots L1′,L2′, respectively, by insertion through the spaces defined between the first and second installation tabs T1′,T2′ and the inner surface IS′ at the rear face RF′ of the shoe (the spring S is optionally also resiliently deformed during this installation process). When the spring S is fully received in the first and second slots L1′,L2′, the spring S and shoe B′ are allowed to relax such that the spring is captured in the spring-receiving region as described above. In order to accomplish this spring installation process, the height of the installation tabs T1′,T2′ must be limited to ensure sufficient space between the tabs T1′,T2′ and the inner surface IS′.
It is generally a preferred solution to use a single-spring S for a blade tensioner where the single-spring tensioner properly controls chain strand vibration over the operating range of the engine and the specified wear life (chain wear take-up) of the tensioner. The excessive dynamics of some engine camshaft drives, however, require the known advantages of a multiple-spring tensioner, i.e., a tensioner including two (or more) metal springs S arranged in a stacked, nested configuration and connected to the plastic shoe as described above to provide the required tensioning load and resilient biasing properties.
Known chain tensioner shoes such as the shoe B′ described above can be deficient with respect to retention of multiple springs in the slots L1′,L2′ under certain conditions. As noted, the height of the installation tabs T1′,T2′ must be limited to allow the spring(s) S to be installed through the gaps defined respectively between the installation tabs T1′,T2′ and the inner surface IS′, and this height limitation decreases the ability of the installation tabs T1′,T2′ to retain more than one installed spring S. Furthermore, the first and second installation tabs T1′,T2′ must be offset in terms of the chain travel direction axis from the first and second side walls W1′,W2′, respectively, in order to manufacture the shoe B′ efficiently in a typical injection molding process. This means that, for each slot L1′,L2′, either its installation tab T1′,T2′ or its side wall W1′,W2′ must be located closer to the open mouth M′ (see FIGS. 5, 5A, 5B) of the slot L1′,L2′, i.e., closer to the other slot L1′,L2′ and closer to the midpoint between the opposite ends B1′,B2′ of the shoe, and this position is referred to herein as the “inboard” position. For the known tensioner shoe B′ shown herein, the first and second installation tabs T1′,T2′ are each located in the inboard position, and the first and second side walls W1′,W2′ are each in the outboard position, i.e., the first and second side walls W1′,W2′ are located a greater distance from the open mouth M′ of the respective slots L1′,L2′ and a greater distance from the midpoint between the opposite ends B1′,B2′ of the shoe B′ as compared to the inboard tabs T1′,T2′. The distance between the inboard first and second installation tabs T1′,T2′ is less that the distance between the outboard first and second side walls W1′,W2′.
FIG. 5 shows the known shoe B′ with first and second springs S (1S,2S) arranged in a stacked, nested relationship and installed in the slots L1′,L2′. FIGS. 5A and 5B provide greatly enlarged views of the opposite ends B1′,B2′ of the shoe B′, and it can be seen that second (outer) spring 2S located closest to the inner surface IS′ of the central portion B3′ is not sufficiently overlapped and retained by either installation tab T1′,T2′. As noted, this is due to the required height limitation the installation tabs T1′,T2′ to allow the spring(s) S to be installed thereover, in combination with the fact that the installation tabs T1′,T2′ are the inboard tabs located where the arched springs 1S,2S are spaced a greater distance from the lower walls LW1′,LW2′ of the respective slots L1′,L2′ as compared to the position of the springs 1S,2S adjacent the outer walls W1′,W2′. In other words, the outer walls W1′,W2′ are respectively located adjacent the opposite distal ends of the springs 1S,2S where the springs contact the lower walls LW1′,LW2′ which enables the outer walls W1′,W2′ to capture the springs 1S,2S, while the inboard installation tabs T1′,T2′, which are necessarily limited in height above the lower walls LW1′,LW2′, are unable to capture the arched portion of the second spring 2S that is spaced away from the respective lower wall LW1′,LW2′. As such, the second spring 2S is at risk of becoming dislodged from either or both slots L1′,L2′ which could allow the spring 2S to contact and undesirably engage the bracket wall MW or to become separated from and/or damage the shoe B′.